PROBLEMS SOLVED BY THE INVENTION
The counterfeiting of articles of many kinds has become a serious problem worldwide, causing great loss of revenues to legitimate businesses and to individuals. Counterfeiting has produced articles that are very difficult to distinguish from the genuine articles, taking sales revenues from the producers of genuine articles and impacting legitimate business' reputations when the counterfeit articles have inferior quality and/or non-existent manufacturers' support. Similarly, problems and losses occur due to counterfeiting of articles used for financial transactions or identification, such as credit cards, drivers' licenses, passports, and immigration documents. Even when genuine articles have been marked with authentication markings such as watermarks, special papers, and holograms which are difficult to replicate, counterfeiters have managed to produce articles that appear genuine. The general availability of newer replication technology such as high-resolution image scanners, laser copiers and printers, and color-accurate color copiers and printers has enabled counterfeiters to produce more credible counterfeit articles. These technological developments of replication hardware continue to make rapid progress, as do the computer hardware and software that support them. Thus it is useful to have additional ways to mark articles for authentication with greater security. Greater security may be achieved by making authentication markings more difficult for counterfeiters to detect and interpret, by incorporating greater complexity into the markings, and by making replication by counterfeiters more difficult. Combining multiple kinds of marking indicia can further increase the complexity of detection, interpretation, and replication, thus providing even better security. Considering the security issue from another point of view, it is not desirable to use the same means that generated the visible appearance of an article to authenticate it, as the visible appearance is becoming easier to replicate. Invisible indicia that cannot be reproduced by common visible graphic copying and printing means can provide improved security, especially when combined with complex images, patterns, and/or characters.